The present invention relates to an electrophotographic recording material comprising an electrically conductive support and a photoconductive layer which comprises a photoconductor, a sensitizing dye, a binder, and customary additives.
In electrophotographic reproduction processes, it is known to use layers comprising zinc oxide as the photoconductor, zinc oxide having a spectral sensitivity in the region of long-wave ultraviolet light, from about 350 nm to about 400 nm. In order to extend the range of spectral sensitivity, these layers are provided with dyes of different chemical types. Such dyes include triphenylmethane dyes, diarylmethane dyes, monomethine cyanines, trimethine cyanines, styryl dyes, oxonols, merocyanines, complex cyanines, azenium dyes, azo dyes, anthraquinone dyes, indigo dyes, vinylene dyes, anthraquinone dyes, indigo dyes, vinylene dyes, azomethines (see e.g., British Pat. No. 1,020,504 and U.S. Pat. No. 3,052,540). Examples of dyes belonging to these classes are Rose Bengale (C.I. 45,440), Acridine Orange (C.I. 46,005), Rhodamine B (C.I. 45,170), Eosin (C.I. 45,380), Fluorescein-Na salt (C.I. 45,350), Brilliant Green (C.I. 42,040) and Pinacyanol (C.I. 808). Other dyes which are used for sensitizing are disclosed in British Pat. No. 1,200,901, U.S. Pat. No. 3,241,959 and German Pat. No. 2,235,408.
German Pat. No. 2,526,720 (corresponding to U.S. Pat. No. 4,063,948) discloses an electrophotographic recording material with an electrically conductive support, which material is used to produce printing plates or printed circuits. The disclosed material comprises a photoconductive layer containing cyanine dyes represented by the formula ##STR1## wherein a is an unsubstituted or substituted indolyl group, phenylamino group, or an indolinyl group and X.sup.- is a monovalent anion. The aforementioned cyanine dyes act with organic photoconductors in the short-wave orthochromatic region, but they are ineffective when used with photoconductor layers comprising zinc oxide.
Other sensitizations achieved in zinc oxide-based photoconductor layers often have the disadvantage that they show a very wide range of spectral sensitization, a phenomenon which particularly occurs, for example, when Eosin, Bromophenol Blue or Rhodamine are used. In addition, residual staining of the photoconductive layer, or of support material comprising, for example, paper, presents another disadvantage. As a result, the recording material has a reduced darkroom safety.
It is also a disadvantage that the sensitization peak is sometimes not sharply pronounced. Frequently, the sensitization peak is not in the region of the strongest emission of the light source used for exposure, which is of critical importance, for example, in a recording material which is to be exposed to laser radiation. In addition, the spectral photosensitivity may often be increased, but the overall sensitivity is reduced or is not improved. In many cases, an adequate sensitization can only be achieved by adding relatively large amounts of dyes, which may impair the chargeability and dark resistivity of the layer. The dyes used also often severely stain the photoconductive layer, which is inconvenient in some fields of application, for example, in copying papers and scaled papers.